A Golgi Study of the Camel Cuneate Nucleus
Article first published online: 29 AUG 2012
Copyright © 2012 Wiley Periodicals, Inc.
The Anatomical Record
Volume 295, Issue 12, pages 2191–2204, December 2012
How to Cite
Zaqout, S. I., Al-hussain, S. M., Al-saffar, R. A. and El-dwairi, Q. A. (2012), A Golgi Study of the Camel Cuneate Nucleus. Anat Rec, 295: 2191–2204. doi: 10.1002/ar.22570
- Issue published online: 17 NOV 2012
- Article first published online: 29 AUG 2012
- Manuscript Accepted: 27 JUL 2012
- Manuscript Received: 11 JUN 2012
- Jordan University of Science and Technology, Irbid, Jordan
Neurons in the cuneate nucleus of the camel brain stem were studied by Golgi method. Six types of neurons were identified based on soma size and shape, density of dendritic trees, morphology and distribution of spines, and appendages. Type I neurons had large spherical somata with somatic appendages. Dendritic appendages were predominant on proximal dendrites with terminal flower-like appendages. Type II neurons had medium to large soma. Appendages and spines were found for the soma as well as along dendrites of different orders. Axons with local branches were seen for these neurons. Type III neurons were small to medium spheroidal or triangulated with large number of spines and appendages on all parts of neurons including soma, dendrites, and initial axonal segments. Axons of these neurons branch profusely and formed rich local axonal arborizations. Type IV medium-size neurons have bipolar, round, or fusiform soma with somatic spines. Their dendrites were sparsely branching with spines and terminal side branches. Type V neurons were spheroid or triangular with small soma with somatic appendages. Their dendrites were sparsely branching and terminate as thin spiny side branches. Type VI neurons were small-size unipolar, round, or fusiform with some dendritic spines and protrusions. These findings shed some light on the structure of the cuneate nucleus of one of the largest animals (the camel). Anat Rec, 2012. © 2012 Wiley Periodicals, Inc.
The dorsal column nuclei (DCN) were studied using different methods such as Golgi impregnation, horseradish peroxidase, Nissl stain, immunocytochemistry, and electron microscope (Chang and Ruch, 1947; Biedenbach, 1972; Gulley, 1973; Blomqvist and Westman, 1976; Corvaja et al., 1978; Berkley et al., 1986; Tan and Gopalakrishnakone, 1986; Crockett et al., 1993). Several neuronal types were described in the DCN in different species such as the frog (Silvey et al., 1974), rat (Basbaum and Hand, 1973; Gulley, 1973), cat (Taber, 1961; Kuypers and Tuerk, 1964; Hand, 1966; Keller and Hand, 1970), and monkey (Biedenbach, 1972). In the frog, for instance, the neuron most frequently seen was a medium-sized cell which measured 10–20 μm in diameter. Over 70% of the neurons in the DCN were of this type. About 15% of the DCN neurons were less than 10 μm in diameter. Large neurons over 20 μm in diameter comprised the remainder of the DCN (Silvey et al., 1974). In the rat, seven different neuronal types were described in the gracile nucleus (Gr) (Gulley, 1973). These types were classified as one small (7 to 10 μ) neuronal type, three intermediate (10 to 18 μ) neuronal types, and three large (22 to 25 μ) neuronal types. In the cat, the areas of the DCN which receive a large inflow of cortical fibres contained many triangular, multipolar, and fusiform cells with long, sparsely ramifying dendrites (Kuypers and Tuerk, 1964). The areas which receive a minimal inflow of cortical fibres in general contained clusters of round cells with many bushy dendrites (Kuypers and Tuerk, 1964). On the basis of soma morphological differences, five cell types were established that occur coextensively throughout the cuneate nucleus (Cu) in the monkey (Biedenbach, 1972). Despite these studies, neuronal classifications according to dendritic pattern and presence or absence of different types of dendritic appandages in the Cu of certain species of large mammals were not described before. Recently, we described six types of neurons in the Gr of the camel (Al-Hussain et al., 2012). No other published studies concerning neurons in the DCN of the camel or any other large mammal were found in published literature. The camel is one of the largest animals on earth. It lives in desert and by tradition; it used to carry heavy weights for long distance. These features of the camel, namely its large size and heavy duties may create need to develop sophisticated balance system including well-developed DCN. This study was an attempt to study the morphological features of different neuronal types in the Cu nucleus of the camel which may open doors for other physiological studies, electron microscopic (EM) studies, and probably other studies of these neuronal types of the brain of this animal which is one of the least studied animals. The aims of this study were to: (1) Identify the different neuronal types in the Cu of the camel and describe their morphological features, (2) Study certain quantitative features of these neurons such as mean diameter of cell body and dendrites of different orders and types of dendritic branching patterns, and (3) Compare these neurons in the camel's Cu with their counterparts in the Gr of the camel and in the DCN of other species. Hopefully, the results of this study will contribute to our understanding of the comparative neuroanatomy of the gracile and cuneate—medial lemniscus system.
MATERIALS AND METHODS
Neuronal types in the Cu of the camel were studied using Golgi method. Brain stems of 10 camels ranging in age from 2 to 4 years obtained from slaughtered camels and fixed in 10% formalin for months. Two Golgi-Kopsch variations (Fox et al., 1951; Braitenberg et al., 1967) were used to stain neurons in transverse sections. Interesting and well-impregnated neurons were studied (drawn, measured and photographed) by using Nikon light microscope equipped with camera lucida, oculometer, and photographing system. Dendritic branching patterns: radiating (give two branches) and tufted (give more than two branches) of different neuronal types were studied. The mean diameters of primary, secondary, and tertiary dendrites of different neurons were measured and compared.
The Cu of the camel brain stem extends from the lower limit of pyramidal decussation; 3 mm below the obex; up to 2 mm above the obex (Fig. 1). The Cu was studied and delineated using hematoxylin and eosin preparations. To characterize further morphological and quantitative features of neurons of this nucleus, blocks of the medulla at the level of the Cu were impregnated by Golgi technique and cut in transverse sections.
The description of the findings of this study will be divided into two main parts, the first deals with morphological characteristics of the different neuronal types found in the Cu and the second pertains to quantitative measurements of selected neuronal parameters in the Cu.
The neurons in Cu were classified according to: (1) soma size and shape, (2) density of dendritic tree, and (3) presence or absence of different types of spines and/or appendages on dendrites and/or cell bodies.
Type I neurons
These neurons (Figs. 2 and 3) represented the largest impregnated neuronal type in the Cu. Their somata mean diameters range from 34 to 47.5 μm (average = 39.70 ± 4.666 μm, n = 20). Their somata exhibited spherical, multipolar, or elongated shape. Somatic spines were commonly seen for these neurons (Fig. 2). Three to five primary dendrites emerged from the cell body of these neurons. These dendrites showed moderate arborizations. Dendrites of these neurons displayed some protrusions, spines, and hair-like appendages which were more prominent on the proximal dendrites. Side branches of different lengths were seen for dendrites of these neurons (Fig. 2). These side branches were either smooth or had some spines. Finally, flower-like dendritic ends were seen for these neurons (Fig. 3). Only the initial axonal segments of these neurons were impregnated in this study (Fig. 2).
Type II neurons
These neurons (Figs. 4 and 5) represented the most frequently impregnated neuronal type in the Cu in this study. They displayed ovoid, elongated, triangular, or multipolar somata. Somatic spines and protrusions were observed for these neurons (Fig. 4). Because of wide range of somata diameters, type II neurons were subdivided into two subtypes. Type IIa (Fig. 4) had large somata with mean diameters ranging from 25.5 to 33.5 μm (average = 29.32 μm ± 2.176, n = 38). Type IIb (Fig. 5) had medium somata with mean diameters ranging from 15 to 25 μm (average = 21.24 ± 2.870 μm, n = 38). The neurons of type II emitted two to six primary dendrites, which unevenly branched. Appendages were found all along the dendritic processes of these neurons: these appendages include small round-like protrusions, grape-like appendages (Fig. 4), or slender stalks with or without spheroidal ending (Fig. 5). Finally, long thin side branches were also found for dendrites of these neurons (Figs. 4 and 5). Axons with several local branches were seen for these neurons (Fig.4).
Type III neurons
These included a small to medium spheroidal or triangular neurons. They were subdivided into two subtypes according to their somata sizes and the density of dendritic tree. Type IIIa (Fig. 6) had medium somata with mean diameters ranging from 16 to 21.5 μm (average = 17.87 ± 1.479 μm, n = 23). Somatic spines and/or protrusions were commonly seen for these neurons. Two to four primary dendrites emerged from the cell body and showed moderate arborization. Spines and appendages of different forms were seen for dendrites of these neurons. These neurons also characterized by the presence of thin side branches of different length with or without spines and protrusions. Initial axonal segment with protrusions were seen for these neurons. Type IIIb (Fig. 7) had small somata with mean diameters ranging from 10 to 15.5 μm (average = 13.30 ± 1.617 μm, n = 20). Somatic spines were seen for these neurons of this type. Two to four primary dendrites emerged from the cell body and their ramification as a whole was generally more extensive when compared with type IIIa. The profuseness of dendritic appendages and the resulting complexity of dendritic arborization give neurons of this type a highly distinctive appearance. The axons of these neurons were identified as processes much thinner than dendrites. These axons originate either from one of the primary dendrites or directly from the cell body itself. They branch profusely and form rich axonal arborizations within the spaces occupied by the dendrites of the parent neurons.
Type IV neurons
These bipolar, round, or fusiform neurons (Fig. 8) had medium somata with mean diameter ranging from 14 to 24.5 μm (average = 19.05 ± 2.886 μm, n = 20). Somatic spines and/or protrusions were seen for these neurons. They had two dendrites that ran in opposite directions and show little branching with some spines. Thin side branches were commonly observed on the terminal ends of these dendrites. Only the initial axonal segments of these neurons were impregnated.
Type V neurons
These spheroid or triangular neurons (Figs. 2 and 9) had small somata with mean diameters ranging from 10.5 to 14 μm (average = 11.83 ± 1.211 μm, n = 6). Somatic spines and/or appendages were commonly seen for these neurons (Fig. 9). Two to three primary dendrites emerge from the cell body. They were sparsely branching and soon terminated with thin spiny side branches. Only the initial axonal segments of these neurons were impregnated.
Type VI neurons
These unipolar, round, or fusiform neurons (Fig. 10) represented the least frequent impregnated neuronal type in this study. They had small somata with mean diameters ranging from 9 to 13.5 μm (average = 1.25 ± 2.327 μm, n = 4). There was little or no dendritic branching with dendritic appendages. Initial axonal segments of these neurons arising from primary or secondary dendrite were seen.
Quantitative parameters of four neuronal types (type I-type IV) in the Cu were studied. The mean diameters of the cell bodies were already included in the first part of this study. Other parameters include: (1) type of dendritic branching pattern: tufted (give more than two branches) or radiating (give two branches) and (2) diameter of primary, secondary, and tertiary dendrites. Table 1 and Fig. 11 show the parameters of neurons I, II, III, and IV.
|Dendrite order neuronal type||Primary||Secondary||Tertiary|
|Cu Type I||50||1||50||33||4||8.25||19||0||–|
|N = 20 cells|
|Cu Type II||190||16||11.9||164||3||54.7||73||0||–|
|N = 76 cells|
|Cu Type III||98||5||19.6||107||1||107||62||0||–|
|N = 43 cells|
|Cu Type IV||38||3||12.7||40||1||40||15||0||–|
|N = 22 cells|
The branching pattern analysis revealed that the radiating pattern was more common than the tufted one in dendrites of different orders of the studied neurons (Table 1). The widths of dendrites of different order showed a wide range of variability of widths of dendrites of different orders as well as of the same order. Wide overlap of diameters was found not only between primary and secondary dendrites but also between primary and tertiary dendrites of the different studied neurons (Fig. 11).
The diameters of dendrites of type I: the primary dendrites range from 1 to 16 μm, the secondary dendrites range from 1 to 9 μm, and the tertiary dendrites range from 0.5 to 5 μm. The diameters of dendrites of type II: the primary dendrites range from 1 to 12 μm, the secondary dendrites range from 0.5 to 9 μm, and the tertiary dendrites range from 0.5 to 5 μm. The diameters of dendrites of type III: the primary dendrites range from 1 to 6 μm, the secondary dendrites range from 0.25 to 5 μm, and the tertiary dendrites range from 0.25 to 3 μm. The diameters of dendrites of type IV: the primary dendrites range from 1.5 to 8 μm, the secondary dendrites range from 0.5 to 5 μm, and the tertiary dendrites range from 0.25 to 3.5 μm.
In camel, at least six main types of nerve cells were found in the Cu in this study. Both similarities and differences were found between these neurons and neuronal types found in the Gr of the camel in our previous study (Al-Hussain et al., 2012) and neuronal types described in previous studies in in the Cu of small mammals such as rat (Basbaum and Hand, 1973) and monkey (Biedenbach, 1972). Unfortunately, neurons in the Cu of large mammals were not described before. Therefore, comparison of neurons in the Cu of the camel with their counterparts in large mammals was not possible.
In general, most of neuronal types observed in the Gr had larger somata and lesser somatic and dendritic appendages comparing to neuronal types observed in the Cu. Although, both of the Cu and Gr nuclei were processed together in the same sections, no very large neurons similar to the very large neurons (somata mean diameters greater than 45 μm and may reach 74 μm) found in the Gr (Al-Hussain et al., 2012) were found in the Cu. Large neurons with somatic mean diameters ranging from 26 to 40 μm include type I and type IIa neurons of the Cu and type II neurons of the Gr. Somatic spines were commonly seen in both neuronal types of the Cu. In contrary, somatic spines were not observed in type II neurons of the Gr (Al-Hussain et al., 2012). In the Cu of the camel, dendritic appendages of different types were observed mainly in the proximal dendrites of type I neurons and along the dendritic processes of type IIa neurons. Conversely, the dendritic tree of the Gr type II neurons were generally smooth with only few number of spines found in the distal dendrites (Al-Hussain et al., 2012). Flower-like dendritic ends were found only in type I neurons of the Cu of the camel. No similar dendritic ends were found in the Gr.
Both of the Cu type IIb neurons and the Gr type III neurons had medium somata diameters ranging from 16 to 25 μm. They displayed ovoid, elongated, triangular, or multipolar shapes. Somatic spines were more detectable in the Cu type IIb neurons than in the Gr type III neurons. The dendritic trees of both types exhibited different types of appendages, but they were obviously denser in the Cu type IIb neurons.
The Cu type III neurons had a small to medium spheroidal or triangulated somata. Somatic spines and/or protrusions were commonly seen in the neurons of this type. The dendrites characterized by rich presence of spines and different shapes of appendages. Thin side dendritic branches were also common in these neurons. Some of these features are comparable with those found in the Gr type IV neurons (Al-Hussain et al., 2012). The soma shape, size, and the presence of somatic spines were found in both neuronal types. The dendritic appendages were clearly more common in the Cu type III neurons than in the Gr type IV neurons. The dendritic trees of both types of neurons showed thin side branches, but these side branches were longer in the Cu type III neurons than in the Gr type IV neurons. An interesting feature of the axons of type III neurons in the Cu was the presence of spinous protrusions for the initial segments. No similar protrusions were seen for the axons of type IV in the Gr.
The small size of type IIIb neurons and the presence of axons branched profusely and formed rich axonal arborizations within the spaces occupied by the dendrites of the parent neurons suggest that these cells are most probably interneurons (Fig. 7). Such branched axons were not observed neither in the Cu type IIIa neurons (this study) nor in the Gr type IV neurons (Al-Hussain et al., 2012). Golgi method is very selective and the degree of completeness of impregnation varies. Therefore, it should be expected in any Golgi study that some type III neurons in the Cu or type IV neurons in the Gr may show impregnated axons with many branches, whereas other cells of the same type may show impregnated axons with only a few branches, and still other cells may appear as axonless cells simply because their axons did not impregnate at all.
Both of the Cu type IV neurons (this study) and the Gr type V neurons (Al-Hussain et al., 2012) share many morphological aspects. These bipolar, round, or fusiform neurons had medium somata with mean diameters ranging from 14 to 24.5 μm. Somatic spines and/or protrusions were seen for some neurons of both types. They had two dendrites that ran in opposite directions. There was little or no dendritic branching. The dendritic tree of these neurons displayed some spines. The only notable difference between the two types was regarding the location of thin dendritic side branches. These were commonly observed on the terminal dendritic ends of the Cu type IV neurons while in the Gr type V neurons they observed at different locations of the dendritic tree.
The Cu type V (this study) shows similarities with neurons of type IVa in the Gr (Al-Hussain et al., 2012). Both of them were small to medium spheroidal or triangulated neurons. Somatic spines and/or appendages were commonly seen. They had two to four primary dendrites with little or no dendritic branching. The dendrites had spines and appendages all along their courses. Thin side branches of different lengths with or without spines were commonly observed on the dendrites of these neurons.
Both of type VI neurons in the Cu (this study) and type VI neurons in the Gr (Al-Hussain et al., 2012) displayed unipolar, round, or fusiform neurons with little or no dendritic branching.
Neurons in the Cu of the monkey (Ferraro and Barrera, 1935) were described as round, oval, elongated, or polygonal. Their somata have short axes range from 4 to 22 μm and long axes range from 9 to 37 μm. Both Ramo'n y Cajal (1909) and Kuypers and Tuerk (1964) found round neurons in the cat Cu with dense, bushy dendrites and neurons with triangular, multipolar, and fusiform cell body and long sparsely ramifying dendrites. These published studies contain little details about neurons in the Cu in monkey and cat. Therefore, it was difficult to compare neurons in the Cu of the camel with their counterparts in these studied species namely the cat and monkey. Since that, neurons in the Cu were not described in any large mammals; comparison of the neurons in the Cu of the camel with their counterparts in other large mammals was not possible.
The flower-like dendritic ends (appendages) found for type I neurons in this study are new findings. No similar appendages were found for any neuronal types in Gr of the camel (Al-Hussain et al., 2012) or for any neuronal types in DCN in other studied species (Kuypers and Tuerk, 1964; Gulley, 1973; Blomqvist and Westman, 1976). These dendritic ends resemble the claw endings described for the dendrites in the granule cells of cerebellar cortex (Weedman and Ryugo, 1996) and dorsal cochlear nucleus (Weedman and Ryugo, 1996; Stuart et al., 2008). Somatic spines for some neuronal types in the Cu were found. Similar somatic spines for some neuronal types in the Gr of the camel were also found (Al-Hussain et al., 2012). No somatic spines were described for any neuronal types in the Cu or Gr of any other studied species.
The branching pattern seems to affect the nerve impulse transmission in different ways (Jon and Jan, 2001). The branching pattern analysis for neurons in the Cu revealed that the radiating pattern was more common than the tufted one in primary, secondary, and tertiary dendrites of all of the studied neurons. Another interesting finding in this study is the wide overlap between the widths of primary, secondary, and tertiary dendrites of all studied neurons in the Cu. These results suggest that at EM level, only the very large and very small dendrites (the dendrites outside the overlap range) can be identified as first-order and third-order dendrites, respectively.
This study demonstrated both similarities and differences between neurons in the Cu nucleus of the camel and the Gr nucleus of the camel and the Cu nucleus of other species. Among these differences are the flower-like dendritic ends (appendages) found for type I neurons in this study, somatic spines and protrusions for the initial segments of some neurons in the Cu of the camel. No similar structures were found in the Cu nucleus of other species (Kuypers and Tuerk, 1964; Gulley, 1973; Blomqvist and Westman, 1976). This may suggest more well-developed Cu nucleus in the camel comparing to the Cu nucleus in other species.
This study demonstrated certain complex morphological features of neurons in the camel Cu. These features include wide variation of somatic and dendritic spines and appendages, flower-like dendritic ends, and spiny axons. This study may provide a background for further studies such as EM studies and immunocytochemistry studies to uncover further details they may improve our comparative neuroanatomy and neurophysiology.
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